The present invention relates to olefin production method using a circulating fluidized bed process.
The olefin like ethylene and propylene is widely used in the petrochemical industry. The olefin can be generally produced from naphtha thermal cracking process. However, because the competitiveness of the process using low-grade hydrocarbon as a raw material becomes higher according to shale gas revolution, on-purpose olefin production method using the catalytic dehydrogenation process is needed.
The catalytic dehydrogenation process for producing the olefin utilizes various low-grade hydrocarbon compound as a raw material, and the olefin yield is very good. However, although commercial fixed bed dehydrogenation process has high olefin yield at an initial stage of the reaction of the hydrocarbon contacting with the catalyst, the hydrocarbon conversion rate and the olefin yield decrease and the energy consumption for the regeneration process is increased because of catalyst deactivation and excessive coke generation as time goes. In order to solve the problem, the circulating fluidized bed process to have short contact time of the hydrocarbon and the catalyst is suggested.
However, at an initial stage of the circulating fluidized bed process to have short contact time of the hydrocarbon and the catalyst, the hydrocarbon reacts with the catalyst to generate the byproduct rapidly other than the olefin. Therefore, there is a demerit that the conversion rate of the hydrocarbon is high but the selectivity of the olefin is very low.
At the circulating fluidized bed process to produce the olefin from the hydrocarbon feedstock, in order to selectively produce the olefin such as ethylene and propylene with high conversion rate and high selectivity, setting the operation condition of Riser mainly conducting the dehydrogenation reaction can be considered as an important factor. Especially, fluid flow phenomena and reaction phenomena in Riser can be easily understood by the following theoretical study, which is explained hereinafter in detail.
As shown in FIG. 1, when gas is provided from the bottom to the reactor charged with the solid catalyst, if particles are fluidized and go over Minimum Fluidization Velocity, Flow Regime would be classified into five (5) regimes.
Specifically, the regimes are named as Minimum Fluidization Regime, Bubbling Fluidization Regime, Slugging Fluidization Regime, Turbulent Fluidization Regime and Lean phase Fluidization with Pneumatic Transport Regime, and the particle motion property in each regime is different from each other.
Therefore, in case of the process using the fluidized bed reactor, the suitable fluidized flow regime for each process property is formed and operated.
FIG. 2 shows the change of the catalyst volume fraction according to the height of Riser, that is, the change of flow regime. It is verified that the catalyst volume fraction in the reactor is changed according to the change of the fluidized flow regime. By the way, because the catalyst volume fraction importantly affects the process performance at the catalytic reaction such as the fluidized contact dehydrogenation reaction, consequently, process operation condition to determine the fluidized flow regime dominating the catalyst volume fraction in the reactor influences very importantly on the reaction result.
In order to determine the fluidized flow regime in Riser of the circulating fluidized bed process, the following factors must be considered. These factors are, for example, catalyst size, catalyst circulating rate, ratio of feed and catalyst, catalyst strength, etc.
In addition, the following factors directly affecting the dehydrogenation reaction must be considered. These factors are, for example, reaction temperature, the amount of absorption heat of the reaction, reaction time, catalyst deactivation caused by coke generation, etc.
At this, during studying the olefin production method using the circulating fluidized bed process with higher economic efficiency and productivity than traditional production process, by applying the catalyst having good selectivity and stability to the circulating fluidized bed process, more efficient olefin production method is developed and the present invention is completed.